Electroacoustical transducer



March 9, 1948. E. E. TURNER, JR

ELECTRO-ACOUSTICAL TRANSDUCER Filed NOV. 18, 1942 2 Sheets-Sheet'l Fxai INVENTOR. EDWIN E. TURNER, JR.

DIAPHRAGM DISTANCE March 9, 1948. E, TURNER, JR 2,437,282

ELECTRQ-ACOUSTICAL TRANSDUCER Filed Nov. 18, 1942 2 Sheets$heet 2 INVENTOR. EDWIN E. TURNER, JR.

tiet entccl Mar. 1948 ELECTROACOUSTICAL '1RANSDUCER Edwin E. Turner, Jr., West Roxbury, Mass., as-

signor, by mcsne assignments, to Submarine Signal Company, Boston, Mass., a corporation of Delaware Application November 18, 1942, Serial No. 466,073

8 Claims. (01. 177-386) The present invention relates to magnetostrictive oscillators of the type disclosed in my prior application Serial No. 677,179, filed June 23, 1933,

Patent No. 2,407,328, issued September 10, 1946,v

in which a great number of magnetostriction tubes are mounted on a radiating plate all acting together to produce a directive beam of high frequency compressional waves and to receive sound,

vibrations coming from the same direction. The apparatus in accordance with the application just mentioned has been very successfully used since its initial development.

The present invention relates to an improvement in the constructional features of an oscillator of the type described in my prior application and also to an improvement in the directivity pattern of the oscillator both in sending and receivine.

In the present invention the magnetostrictive tubes are mounted and secured in the radiating plate, but all of the other elements of the oscillator are supported by the back of the casing and or come out with the back cover through which all the electrical connections are made.

An added feature of the present invention is the arrangement of the magnetic circuit whereby the magnetostrictive elements are polarized. Permanent magnet elements are supported by the back case which provides a low reluctance path for the magnetic flux. These permanent magnet elements are aligned to fit in recesses in the radiating plate which is also of magnetic material and provides thereby a low reluctance flux path to the ends of the magnetostrictive tube, one end of which, as has been stated, is attached to the radiating plate and the other end of which is recessed in the back supporting cover supporting the magnetizing element.

A further advantage of the present invention is the method of energizing the magnetostrictive tubes by means of individual coils out of contact with the magnetostrictive tubes and supported by the, back cover in such a manner that groups of tubes within annular sectors of the radiating member are connected so as to provide the desired energy to control'the beam pattern whereby secondary lobes of radiation are reduced. In obtaining this effect the coils surrounding annular groups of magnetostrictive units may be connected in series, the number of units in the group providing the desired impedance so that the driving energy per unit surface in each annular ring is such as to correspond to the desired beam pat tern characteristic.

l A still further advantage in the construction according to the present invention is that the oscillator may be used in deep water where the hydrostaticpressure on the diaphragm is high. For

this purpose the beam pattern characteristic of the radiating face of the oscillator is designed on thebasis of having a clamped edge unit with a zero amplitude at that point. This permits the diaphragm or radiating element acting as the front cover for the oscillator to be substantially uniformin thickness Without any compliance web in the vicinity of its clamping edge, thus eliminating structural weaknesses and permitting operation of the oscillator under very large hydrostatic pressures. In addition to this feature of the design the permanent magnet elements may serve also as stop members to limit maximumamplitude of displacement of the radiating face due to shock.

Other and further advantages of the present invention will be more readily understood from a consideration of the specification below describing an embodiment of the same when taken in connection with the drawings in which Fig. 1 a

tion on the line 2--2 of Fig. 1; Fig. 3 shows a detail, illustrating the means of obtaining power distribution for the desired beam pattern; Fig. 4 shows characteristic curves of diaphragm amplitude distribution natural and forced; and Fig. 5 shows a calculated beam pattern of an oscillator of the present type.

In the drawings the oscillator comprises the radiating member or diaphragm l which is clamped at its periphery 2 by means of a group of bolts 3 spaced around the periphery of the radiating member. The bolts 3 thread into a cylindrical wall 4 of the casing which at one end furnishes the clamping surface for the diaphragm or radiating member and at its other end, which may be considered the back end, furnishes a clamping surface for the back cover 5. The cylindrical wall 4 is made of some material such as bronze non-magnetic steel or the like which has a comparatively low permeability to magnetic flux. The back cover 5 is held to the cylindrical wall 4 by a series of bolts 6 spaced about its pethese tubes are spaced over the whole diaphragm and cooperate to vibrate the diaphragm under the same principles which are described in my prior patent application referred to above. Other means may be used to hold the tube I firmly to the plate I. The tube 1, as has been stated, is of suitable magnetostrictive metal with a comparatively high magnetostrictive effect and the plate I is preferably of iron or steel having a high flux permeability. The tubes 1, as shown in Fig. 1, extend upward into recesses 8 formed in the cover 5, which cover is also preferably of iron or steel having a high flux permeability. The recesses 8 formed from the inside surface of the cover 5 are aligned concentrically with the axes of the tubes I and the tubes 1 are given sufllcient working room within these recesses. The recess 8 also carries and supports the coil form 9 which has a collar or flange I fitting snugly against the walls of the recess.

A coil form is also provided with a shoulder ll resting against the inner surface of the cover 5. A coil I2 is woundon this coil form and serves tocarry the alternating current at the desired frequency for furnishing the driving power for the magnetostriotive tube. This coil l2 may be and usually is also used for receiving, in which case the vibrations of 'the tube I generate a potential in the coil l2. The coil l2 may have a polarizing current for initially polarizing the magnetostrictive tubes. However, as indicated in Fig. 1, means for this is provided by the permanent magnet rods l3 which may be of some well-known material capable of providing a powerful permanent magnetic field such, for instance, as metal usually known under the trade name of Alnico.

The permanent magnets I3, as indicated in Figs. 1 and 2, are spaced alternately between the magnetostrictive tubes all over the back cover so that the magnetic flux will find a lower reluctance path through the magnetrostrictive tubes than through the air. These permanent magnets I3 may be all magnetized simultaneously by placing temporarily a large magnetizing coil external of the wall 4 of the oscillator so that the polarity of each of the magnets I3 is in the same direction. The permanent magnets l3 are firmly held by a forced fit joint or otherwise in recesses 14 extending into the back cover 5 from its inner surface. These permanent magnets l3 also extend into recesses I5 in the plate member I and are concentric with such recesses but spaced from the walls of the recess so that when the back cover 5 is removed, the permanent magnets 13 remain with the back cover. An insulating plate [6 with suitable perforations so as to permit the projection of the magnetostrictive tubes and the permanent magnets is positioned on the lower face end of the coil forms and serves to separateand insulate all the coil elements from the diaphragm or plate I. casing formed by the elements described may be put under gas pressure through the plug l8.

As will be seen from Fig. 2 the inner face of the oscillator carries a great number of magnetostrictive tubes which serve to drive the diaphragm or radiating member at these particular points. Other electrically operated means may be used to drive the diaphragm, but magnetostrictive driving means have certain advantages in obtaining the desired power distribution. The small portion of the plate surrounding each tube is substantially driven by the tube with the same amplitude as the portion of the plate right over the tube and the tubes are spaced close enough The chamber l1 within the together over the whole diaphragm so that the diaphragm as a whole may be driven at amplitudes determined by the driving force on the tubes.

It is well known that diaphragms and plates have natural modes of vibration. The frequency and natural modes of vibration of any radiating member depend upon its shape, thickness, size, the places at which it is retained or held and the points at which it is driven. Large plates, other things being equal, have lower frequencies of vibration than smaller plates, and in the range of supersonic frequencies where large plates or diaphragms are used, the natural frequency of vibrations of the plates is usually well below the supersonic frequencies at which the oscillator is to work. This condition prevails in the present application where the high frequencies are of the order of 12-30 kilocycles and the linear dimensions of the radiating plate are of the order of 16 inches. With a steel plate 16 inches in diameter, clamped at its edges, and of an inch i cycles per second. This natural mode of vibration is such, when excited at the center only, as to produce a maximum amplitude at the center with amplitudes decreasing to zero towards the clamping edges. The magnetostrictive tubes in the present invention are preferably Wound with the same number of turns to provide the same impedance and are so disposed upon the diaphragm and connected together in series parallel groups such that when excited through the same or equal voltage source, the amplitude of the diaphragm over its surface approximates in steps the characteristic of the natural mode of vibration when the plate is struck at the center. Since the diaphragm is continuous and preferably uniform in thickness, the elasticity of the material of the diaphragm converts the discontinuity of the step energization to a continuously varying motional amplitude approximating more closely the desired, characteristic curve. The diaphragm will most easily move in this fashion and the vibration of this type will produce a desirable beam pattern such that the center lobe has a comparatively great intensity and the auxiliary lobes a comparatively very small intensity, over the beam pattern produced in the ordinary manner by excitation substantially uniformly over the whole diaphragm surface.

In Fig. 3 the diaphragm is sectioned off in sections A, B, C, D and E, the section at A being driven by one group of tubes whose exciting coils are all connected in series and similar also sections B, C, D and E will likewise be driven by series connected units. It is not essential, however, that these units all be connected in series, the essential feature being that the impedance of each unit be such as to produce the desired amplitude of this section corresponding to the free mode characteristic curve illustrated by X in Fig. 4 where the ordinate represents the amplitude of motion of the plate or vibrational diaphragm at a point on the diameter of its radiating face corresponding to the abscissa/axis of Fig. 4, which 0, D and E respectively, the excitation of A being greatest, B and C equal with steeper steps for D and E respectively. It is obvious the other step curvesmay be used as approximations of the curve X and that the diaphragm may be divided up into more rings whereby the step curves may be made to diverge less from the curveX.

The beam characteristic of the oscillator is shown in polar dec bel coordinates in Fig. in which there is a main beam K with two small auxiliary lobes L1 and L2 fardown in intensity from K to such an extent that they will not interfere with the main beam.

Having now described my invention, I claim:

1. An oscillator for transmitting or receiving directively high frequency compressional waves comprising a radiating plate having linear dimensions large as compared to the wave length of a compressional wave to be transmitted or received in the propagating medium, means clamping said radiating plate in its periphery and means for vibrating said plate, said means acting over the surface of the same for producing amplitudes at points of the surface of said plate corresponding approximately to the law of lowest natural mode of vibration of the same whereby a directive beam pattern is obtained with an emphasized main lobe and suppressed auxiliary lobes.

2. An oscillator for transmitting or receiving directively high frequency compressional waves comprising a radiating plate of uniform thickness having linear dimensions large as compared to the wave length of a compressional wave to be transmitted or received in the propagating medium, means clamping said radiating plate in its periphery and means for vibrating said plate, said means acting over the surface of the same for producing amplitudes at points of the surface of said plate corresponding approximately to the law of lowest natural .mode of vibration of the same whereby a directive beam pattern is obtainedwith an emphasized main lobe and suppressed auxiliary lobes.

3. An oscillator for transmittin or receiving directively high frequency compressional waves comprising a radiating plate having linear dimensions large as compared to the wave length of a compressional wave to be transmitted or received in the propagating medium, means clamping said radiating plate in its periphery, means nected to said plate for vibrating the same and means for energizing said magnetostrictive elements in accordance with a chosen. amplitude characteristic corresponding approximately to the lowest natural mode of vibration of the plate whereby a directive beam pattern is obtained with an emphasized main lobe and suppressed auxiliary lobes.

4. An oscillator for transmitting or receiving directively high frequency compressional waves comprising a radiating plate having linear dimensions large as compared to the wave length of a compressional wave to be transmitted or received in the propagating medium, means clamping said radiating plate in its periphery, means for vibrating said plate comprising a plurality of active magnetostrictive elements operatively connected to said plate for vibrating the same, energizing coils for each of said magnetostrictive elements, said energizing coils for magnetostrictive elements spaced within concenfor vibrating said plate comprising a plurality of active magnetostrictive elements operatively contrio ring portions of said plate being connected together whereby equalized vibrational amplitudes are,provided for chosen ring portions of said plate corresponding approximately to the lowest natural mode of vibration of the same whereby a directive beam pattern is obtained with an emphasized main lobe and suppressed auxiliary lobes.

5. A magnetostrictive oscillator for transmitting or receiving directively high frequency compressional waves comprising a radiating plate having linear dimensions large as compared to the wave length of the compressional wave to be transmitted or received in the propagating medium, a great number of magnetostrictive tubes rigidly attached to the surface of the plate not exposed to the sound-propagating medium, means enclosing said plate forming a casing whereby one surface of the plate is not exposed to the soundpropagating medium, means rigidly clamping said plate at its peripheral margin to said casing, said casing having a back cover, energizing coils for each magnetostrictive tube surrounding the same, means supporting said energizing coils from said back cover out of contact with said magnetostrictive tubes, permanent magnet means also supported in said cover and extending downward to said radiating plate, said permanent magnets being distributed over the whole back cover, the cover and radiating plate being of material permeable to magnetic flux. l

6. An oscillator for transmitting or receiving directively high frequency compressional waves comprising a casing having two opposed cover elements of materials permeable to magnetic flux, one serving as a radiating plate, a great number of magnetostrictive tubes mounted rigidly in said radiating plate, individual coil elements for energizing said magnetostrictive tubes and a great number of permanent magnet elements supported in positions parallel to said magnetostrictive tubes between the cover and the radiating plate and furnishing polarizing means for said magnetostrictive tubes, said coil elements and tubes having substantially the same electrical impedance, and means connecting in series coils of annular groups concentric with the center of the plate for directively energizing said oscillator,

'7. An oscillator for transmitting or receiving directively high frequency compressional waves comprising a casing having two opposed cover elements of materials permeable to magnetic flux, one serving as a radiating plate, a great number of magnetostrictive tubes mountedrigidly in said radiating plate, individual coil elements for energizing said magnetostrictive tubes and a great number of permanent magnet elements supported in positions parallel to said magnetostrictive tubes between the cover and the radiating plate and furnishing polarizing means for said magnetostrictive tubes, said coil elements and tubes having substantially the same electrical impedance, and means connecting in series coils or annular groups concentric with the center of the plate for directively energizing said oscillator, said annular groups acting over the surface of the radiating member for producing amplitudes at points of the surface of said radiating member corresponding approximately to the law of lowest natural mode of vibration of the same whereby a, directive beam pattern is obtained with an emphasized main lobe and suppressed auxiliary lobes 8. In an electro-acoustioal transducer, the combination of an acoustic diaphragm, a magnetic member disposed in spaced relation thereto, and a. plurality of magnetostrictive elements secured to said diaphragm at spaced points thereon, said magnetic member being provlded with a plurality of recesses therein corresponding in number to the number ofsaid elements, and said elements extending into said recesses a distance short of the depth thereof, there being also a slight clearance between said elements and the surfaces of said member defining said recesses.

EDWIN E. TURNER, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Steinberger Dec. 15, 1936 Number OTHER. REFERENCES Ser. No. 382,084, Menges (A. P. C.), published May 18, 1943, now abandoned. 

